Anchor system

ABSTRACT

921,336. Storing liquefied gas. CHICAGO BRIDGE &amp; IRON CO. June 13, 1961 [Dec. 14, 1960], No. 21220/61. Class 8(2). [Also in Group XXIX]. A storage tank for liquefied gas, for example, comprises an inner storage vessel 12 and an outer shell 11 spaced from the vessel 12, the latter being anchored by substantially vertical tie bars 38 which are connected at their upper ends to the vessel 12 and extend downwardly through a foundation 15 for the vessel 12 to a laterally extending beam structure 30 underlying but spaced from the vessel 12. The foundation 15 which may comprise layers of perlite concrete rests upon the bottom 19 of the shell 11. Heating coils (not shown) may be provided in the ground to prevent it freezing. The outer shell is supported on concrete 16 to which it is anchored by bolts 17. The beam structure 30 comprises a plurality of beams 31 attached to the outer shell 11 and, optionally, a circular ring 32 and cross beams 33. The tie bars 38 are disposed so as to be free to bend when the vessel 12 expands or contracts, or rigid tie rods may be provided which are fitted with rollers. In a second embodiment, Fig. 11 (not shown), the inner vessel foundation comprises a layer of perlite concrete upon a rigid insulation layer which is disposed above a layer of reinforced concrete; the tie bars are secured in the latter and extend through holes passing through the other two layers, the holes containing resilient insulation material. The tank may be used for high temperature storage service where the inner vessel is subject to gas pressure.

March 1962 J. T. HORTON ETAL 3,

ANCHOR SYSTEM Filed Dec. 14, 1960 4 Sheets-Sheet 1 INVENTOR.

March 20, 1962 J. T. HORTON ETAL 3,025,993

ANCHOR SYSTEM Filed Dec. 14, 1960 4 Sheets-Sheet 2 March 20, 1962 J. T. HORTON ETAL 3,02

ANCHOR SYSTEM 4 Sheets-$heet 3 Filed Dec. 14, 1960 INVENTORS.

March 20, 1962 J. T. HORTON ETAL. 3,

ANCHOR SYSTEM Filed Dec. 14, 1960 4 Sheets-Sheet 4 IN VEN TORS. j0j2mfM 3,ti25,993 ANCHGR SYSTEM .Iohn T. Horton, Chicago, and Ivan V. La Fave, Hornewood, IEL, assignors to Chicago Bridge dz Iron Gompany, Chicago, Ill., a corporation of Iliinois Filed Dec. 14, 196i), Ser. No. 75,7tl4 S? (Ilaims. (Cl. 22015) This invention relates to liquid storage vessels. It is particularly directed to a double walled storage tank structure having an inner storage vessel so tied to the tank structure foundation as to counteract the uplifting force caused by internal gas pressure within the inner vessel. It is especially well adapted to the storage of liquefied, normally gaseous material such as methane, propane, oxygen, ammonia and the like at reduced tem peratures.

In the storage of liquefied gases a preferred system employs a slight superatrnospheric pressure within the storage vessel to insure the proper operation of the storage tank, accessories and control equipment. An internal pressure of l to 2 p.s.i.g. is adequate to effect the positive operation of the control valves, refrigerating units, and other mechanical equipment. Refrigerated storage under these conditions can be advantageously and economically efiected in an insulated, double-walled storage tank structure having a substantially flat-bottomed, cylindrical, inner storage vessel.

In the construction of double-walled storage structures employed in this invention, the inner storage vessel comprises a bottom which can be substantially flat, or dished, sloped to facilitate drainage, sidewalls which can be polygonal, barrel-shaped or preferably right circular cylindrical, and a roof to complete the enclosure. The sidewall rests on or near the periphery of the bottom, which, in turn, overlays and rests on a suitable foundation, and is spaced above the bottom of the outer vessel. Generally, the metal plate used for the construction of the bottom is thinner than the sidewall at the intersection with said bottom because the hydrostatic pressure from the liquid contents is transmitted directly through to the foundation and the bottom is not subjected to significant tensile stresses. A similarly shaped outer vessel is constructed spaced apart from the inner vessel to enclose the inner vessel and provide an insulation space to insulate the inner vessel from the exterior atmosphere.

In such tanks the use of even a slight internal pressure in the order of 1 to 2 p.s.i.g. creates an uplift problem by acting against the inner vessel roof, tending to lift the shell and, in turn, the periphery of the bottom. For example, in a fiat-bottom cylindrical tank having an inner storage vessel with diameter of 100, enclosed by a similar outer vessel 106' in diameter and used for the storage of liquid propane at t) F., with an internal pressure in the inner vessel of 1 p.s.i.g., the resulting uplift force is 1,130,000 lbs. With the sidewalls and roof of the inner storage vessel constructe from steel plate of thickness in accordance with conventional design and using A" thick steel plate for the bottom, it becomes necessary to tie down the inner tank against an uplift force caused by the 1 p.s.i.g. operating pressure which otherwise would induce undesirable bending stresses in the peripheral margin of the tank bottom. This invention employs an anchorage system which retains the desired heat leak characteristics of an insulated foundation and provides flexibility adequate to permit thermal changes in dimensions.

Referring to the drawings:

FIGURE 1 is a cross-sectional plan view of an. embodiment of a flat-bottomed tank of this invention taken along line l1 of FIGURE 2.

3,Z5,93 Patented Mar. 20, 1952 FIGURE 2. is a cross-sectional view in reduced scale of the tank-of FIGURE 1 taken along line 22.

FIGURE 3 is an enlarged fragmentary View of one embodiment of the anchorage system.

FIGURE 4 is a crosssectional plan view taken along line 44 of FIGURE 3 of the beam structure framework used in the anchorage system.

FIGURE 5 is a cross-sectional elevation View taken along line 5-5 of FIGURE 3 of the inner tank anchor bolt and anchor lug used in the anchorage system.

FIGURE 6 is a cross-sectional elevation view taken along line 66 of FIGURE 5 of the outer shell anchor bolt and anchor lug assembly used in the anchorage system.

FIGURE 7 is a fragmentary detail taken along line 7-7 of FIGURE 5 of the inner tank anchor bolt lug used in the anchorage system.

FIGURE 8 is a fragmentary detail taken along line 83 of FIGURE 5 of a cut-out in the inner vessel bot tom for the anchor bolt used in the anchorage system.

FIGURE 9 is a cross-sectional fragmentary View of FIGURE 5 taken along 99 of the void provided in the concrete foundation for the inner vessel.

FIGURE 10 is an enlarged fragmentary cross-sectional view of an embodiment of the inner storage vessel anchorage system.

FIGURE 11 is a fragmentary cross-sectional view of an alternative anchorage system constructed in accordance with this invention.

Referring to the attached drawings, FIGURES 1l0 show an illustrative embodiment of a storage tank structure having a substantially flat-bottom inner storage vessel It) used in connection with this invention. The outer shell 11 which is spaced apart from the inner storage vessel 12 provides a vapor barrier which prevents atmospheric water vapor from penetrating the insulation system 13 causing a loss of its insulating qualities. The inner vessel 12. contains the stored product L and rests on inner vessel foundation 15 which comprises load-bearing insulation in the form of layers of perlite concrete, reinforwd or unreinforced concrete, rigid insulation and others or combinations thereof. The inner vessel foundation 15' rests upon outer vessel bottom 19 which is a vapor barrier and which is supported by the graded subbase. The depth and kind of material used in the foundation 15 depends upon the storage temperatures involved and the loads to be supported. If the foundation 15 is not sufficiently insulated, or the subbase is not heated or ventilated in some Way, the ground water under the tank can freeze and substantial failure of the soil subbase may result. If desired, heating coils, not shown, can be imbedded in the ground to prevent freezing. Generally, the insulation is required to keep heat leak to a minimum and thereby reduce evaporation losses.

The concrete ringwall 16 is provided as a foundation for the tank assembly 10 and to provide support for the outer shell 11. A plurality of peripherally spaced, outer shell, anchor bolts 17 for the outer shell conventionally imbedded in the concrete ringwall 16 hold the outer shell 11 in position and inhibit any upward movement thereof. The anchor bolts 17 are connected to the sidewall 18 and bottom 19 of outer shell 11 by means of anchor bolt lugs 20 commonly used in tank construction where anchor bolts are subjected to both bending and tensional forces. Other suitable connecting means can also be used, such as a circumferential ring attached at or near the base of the outer shell 11.

The inner storage vessel 12 comprises a sidewall 21 enclosed by a roof 22 and a bottom 23. The inner vessel is conventionally designed such that the tank bottom is relatively thin. Accordingly,.the vessel bottom tends to be bent upward about its periphery when a slight superatmospheric pressure is acting in the vapor zone over the stored product, on account of the uplift transmitted from the roof through the sidewalls and the bottom to sidewall connection. To counteract this effect, the inner vessel tie down system of this invention is employed.

7 In the illustrated embodiment, shown in FIGURES l- 10, a framework anchored in the inner vessel foundation 15 such as a beam structure 30 is provided to distribute the uplift force transferred from the inner vessel 12 to the foundation 15. The illustrated outwardly extending beam structure 30 comprises a plurality of beams 31 attached to the sidewall 18 of the outer shell 11 in order that the weight of the outer shell 11 can be utilized to counteract the uplifting of the inner vessel 12. Circumferential ring 32 or cross beams 33 can be provided if the area of the beam assembly 30 is not suflicient to keep the bearing load on the foundation 15 suficiently low. Any suitable load distribution layout may be substituted for the configuration shown and any suitable structural members may be substituted for the radial beams shown.

The length and size of the beams 31 are determined by balancing the force of the internal pressure acting on the beams 31 and the dead Weight of the surrounding materials including the outer shell 11 against the position and upward thrust of the tie rod-s 35 of inner vessel anchor lug assembly 39. The peripheral ring 32 and the transverse beams 33 are included only when more surface area is needed to resist the upward thrust of the tie rods .38 than that provided by the beams 31.

The anchor lug assembly 39 comprises a pair of spaced side plates 40 and 41 secured to the sidewall 21 and the portion of bottom 23 projecting beyond the sidewall 21 of inner vessel 12, and a continuous pad ring 4-2 mounted atop the spaced side plates 40 and 41 and extending pe- 'ripherally about the outer face of the sidewall 21 of inner vessel 12. Cooperating apertures are provided in the pad ring 42 to permit movement of the tie rods 38 occurring during thermal expansion and contraction of the inner vessel 12 resulting during the filling and emptying phases of the storage cycle. Transverse holes 45 are used to provide access to the apertures in beams 31. Suitable forms such as cardboard tubes 46 used during the concrete casting to form the apertures can be left in place as p The inner vessel anchor lug assembly 39 increases the length of the tie rods 38. Because the rate of heat transfer is inversely proportional to the length and directly proportional to the cross-sectional area of the heat path, heat gained by the inner tank will be minimal.

The long tie rod 38 which is preferably constructed of a material which will remain flexible or ductile without loss of tensile strength at operating temperatures, is provided not only because of its long heat transfer path but for its flexibility to accommodate to the lateral thermal contraction and expansion of the inner tank 12. Alternate tie rods such as a rigid tie rod on a plate fitted with rollers such that the inner tank could thermally expand and contract without requiring the tie rod to bend at all can also be used. In any such means, however, an allowance must be made for thermal movement of the inner vessel without destroying the structural integrity of the entire system. For example, in the storage of liquid propane at about 44 F. with the inner vessel being fabricated from A-30O class 1 steel (ASTM A201 grade B), the tie rod can be fabricated from ASTM A320 grade L-7 steel. As another example, in some circumstances where the product is stored at a very cold temperature, such as oxygen at 297 F., the tie rod 38 can be fabricated from ASTM A320 grade l18 or ASTM A276 type 304 grade steel whereas the inner vessel 12 can be of aluminum or stainless steel. The movement of the inner vessel 12 is substantial during the emptying and filling operations at that extremely low temperature and the tie rod 38 must be able to flex accordingly or an undesirable degree of restraint will be induced at the tank shell.

Another embodiment of the anchorage system is shown in FIGURE 11. As in the above-described flat-bottom, double-wall tank, inner vessel 52 and an annular space fiiledwith insulation are employed. in this embodiment, a cryogenic liquid, such as liquid methane, is stored as the liquid L. At 1 p.s.i.g., methane must be stored at or below 250 F. and therefore, the insulated foundation 55 is much deeper than the foundation shown in FIGURES 1 and 2 or else is constructed of material having higher insulation value. The illustrated foundation 55. comprises a layer of perlite concrete 56, rigid insulation 5'7 and a reinforced concrete layer 58 in which the tie rod 62 is secured. An elongated hole 59 through which the tie rod 62 extends traverses the layers of concrete and insulation 57. A resilient insulation 61 disposed within hole 59 surrounds the inner vessel tie rod 62 so that considerable lateral movement of the tie rod can take place when inner vessel 52 thermally expands and contracts. The shear key 63 laterally extending from the inner face of the wall is provided so that the concrete SS is tied firmly to the outer shell 51. Embedded in concrete 53 are reinforcing bars 64 and 65. The reinforcing bars 64 and 65 give the concrete 58 sufficient beam strength to counteract the upward thrust of tie rod 62. The same principles are used to design the concrete beam structure system of the alternative embodiment shown in FIGURE 10 as those used to design the beam structure 30 as shown in FIGURES 1 and 2. A suitable foundation 66 is used to support the storage tank structure. Anchor bolts 67 secure the structure to the foundation with the aid of peripheral pad ring 68. A similar pad ring 69 is used for the inner vessel anchor lug.

The instant invention has especial application in the storage of liquefied gases such as propane, methane, oxygen, ammonia, etc., in tanks having capacities within the range of 200,000 to 10,000,000 gallons. This inven tion however, can be employed in other storage services (for example, for high temperature service) in a variety of tank sizes wherein the storage vessel is subject to an uplifting force caused by internal gaspressure within the inner vessel concomitant with thermal-induced expansion and contraction of the storage vessel.

In the construction of the tank and anchorage system of this invention conventional materials of construction can be used. For low temperature service those structural elements exposed to low temperature should be fabricated from stainless steels, nickel alloy steels, or other materials which are not deleteriously embrittled at the low temperatures experienced. Granular, shredded, or other particulate insulation can be used in the insulating space. Perlite, for example, is an excellent low temperature insulation.

For simplicity, the various auxiliary equipment and piping associated with the filling, emptying, venting, etc., of storage tanks are not shown because piping arrangements not affectng the instant invention can be used. Accordingly, although the instant invention has been described with reference to the foregoing specific embodiments, it is evident that variations and modifications can be made by those skilled in this art without departing from the scope of this invention.

What is claimed is:

1. In a storage tank structure comprising an inner storage vessel having a bottom and sidewall and a roof and an outer shell having a walled portion surrounding and spaced apart from said inner vessel to provide a vapor barrier and an annular insulating space, said inner vessel being subject to uplift forces resulting from pressure within the inner vessel; a system for securing said inner vessel within said structure comprising a laterally extending beam structure underlying said inner storage vessel and spaced therebelow, said beam structure being connected at its outer edges directly to said walled portion, and a plurality of elongated substantially vertical ties peripherally spaced about said side wall and fastened at their upper ends to said inner vessel adjacent the connection between its bottom to sidewall and at their lower ends to said beam structure, said ties being laterally free to permit lateral movement of said inner storage vessel.

2. In a storage tank structure comprising an inner storage vessel having a bottom and sidewall and a roof and an outer shell having a walled portion surrounding and spaced apart from said inner vessel to provide a vapor barrier and an annular insulating space, said inner vessel being subject to uplift forces resulting from pressure within the inner vessel; a system for securing said inner vessel within said structure comprising a laterally extending beam structure underlying the periphery and extending inwardly from said inner storage vessel and spaced therebelow, said beam structure being connected at its outer edges directly to said walled portion, and a plurality of elongated substantially vertical ties peripherally spaced about said sidewall and fastened at their upper ends to said inner vessel adjacent the connection between its bottom to sidewall and at their lower ends to said beam structure, said ties being laterally free to permit lateral movement of said inner storage vessel.

3. In a storage tank structure comprising an inner storage vessel having a bottom and sidewall and a roof and an outer shell having a walled portion surrounding and spaced apart from said inner vessel to provide a vapor barrier and an annular insulating space, said inner vessel being subject to uplift forces resulting from pressure within the inner vessel; a system for securing said inner vessel within said structure comprising a laterally extending beam structure underlying said inner storage vessel and spaced therebelow, said beam structure being connected at its outer edges directly to said walled portion and a plurality of elongated substantially flexible vertical ties peripherally spaced about said sidewall and fastened at their upper ends to said inner vessel adjacent the connection between its bottom to sidewall and rigidly secured at their lower ends to said beam structure, said ties being laterally free to permit lateral movement of said inner storage vessel.

4. In a storage tank structure comprising an inner storage vessel having a bottom and sidewall and a roof and an outer shell having a walled portion surrounding and spaced apart from said inner vessel to provide a vapor barrier and an annular insulating space, said inner vessel being subject to uplift forces resulting from pressure within the inner vessel; a system for securing said inner vessel within said structure comprising a laterally extending beam structure underlying the periphery and extending inwardly from said inner storage vessel and spaced therebelow, said beam structure being connected at its outer edges directly to said walled portion, and a plurality of elongated substantially flexible vertical ties peripherally spaced about said sidewall and fastened at their upper ends to said inner vessel adjacent the connection between its bottom to sidewall and rigidly secured at their lower ends to said beam structure, said ties being laterally free to permit lateral movement of said inner storage vessel.

5. An anchorage structure for tying down the periphery of a bottom of a closed inner vessel adapted to store liquid under pressure, where said inner vessel is a portion of a double walled tank comprising said inner vessel and an outer shell of similar conformation to said inner vessel completely surrounding and spaced apart from said inner vessel, said system comprising in combination a plurality of elongated, thin, flexible, substantially vertical ties connected at their upper ends to said inner vessel adjacent the connection of said bottom to the sidewalls of said inner vessel and rigidly connected at their lower ends to a laterally extending beam structure underlying the periphery of said bottom and spaced therebelow, said beam structure being fixed at its outer periphery to the sidewalls of the outer vessel, whereby said inner vessel is left free to expand or contract laterally due to thermal variations therein, said expansion and contraction being accommodated in said vertical ties by lateral movement thereof, but said inner vessel is restrained against vertical movement caused by uplift forces resulting from the internal pressure acting against the roof of said inner vessel and transmitted through the sidewalls to the bottom to sidewall connection, such restraint being provided by the axial strength of said vertical ties, the uplift forces resulting from said pressure being counteracted by the weight of said beam structure, the weight of the outer vessel acting upon said beam structure, and the weight of insulating material positioned in the annular space between said inner vessel and said outer vessel.

6. In a storage tank structure comprising a cylindrical inner storage vessel having a substantially flat bottom, a cylindrical sidewall and a roof, said bottom being fab ricated from a metal thinner than the sidewall at the in tersection with said bottom, and an outer shell having a Wall portion surrounding and spaced apart from said vessel to provide an insulating space, said outer shell being mounted on and anchored to a suitable foundation; a system for securing said inner vessel to said structure which comprises a beam structure underlying said inner vessel, and including a monolithic foundation upon which said inner vessel is directly resting overlying said beam structure, said beam structure comprising a plurality of radially disposed structural elements, being connected directly to the walled portion of said outer shell, said foundation being provided with a plurality of tubular holes peripherally spaced about the bottom of said inner vessel and traversing said foundation between said beam structure and said insulating space, and a plurality of elongated tie rods affixed at one end to said beam structure and extending through said tubular holes and connected at the other end to said inner vessel adjacent the connection between the sidewall and bottom of said inner vessel to interconnect said beam structure and said inner vessel, the cross-sectional area of said bolts being less than the cross-sectional area of said holes whereby lateral displacement of said tie rods is permitted.

7. In a storage tank in accordance with claim 6 in which the inner ends of said structural elements terminate short of the center of said vessel and are interconnected by a ring structural element.

8. In a storage tank in accordance with claim 6 in which said tie rods are flexible members rigidly attached at one end to said beam structure.

9. In a storage tank structure comprising a cylindrical inner storage vessel having a substantially flat bottom, a cylindrical sidewall and a roof, said bottom being fab= ricated from a metal thinner than the sidewall at the intersection with said bottom, and an outer shell having a wall portion surrounding and spaced apart from said vessel to provide an insulating space, said outer shell being mounted on and anchored to a suitable foundation; a system for securing said inner vessel to said structure which comprises a beam structure underlying said inner vessel including a monolithic foundation upon which said inner vessel is directly resting overlaying said beam structure, said beam structure comprising a concrete beam being connected directly to the wall portion of said outer shell, said foundation being provided with a plurality of tubular holes peripherally spaced about the bottom of said inner vessel and traversing said foundation between said beam structure and said insulating space, and a plurality of elongated flexible tie rods rigidly aflixed at one end to said beam structure and at the other end to said inner vessel adjacent the connection between the bottom and sidewall of said inner vessel, the cross-sectional area of said bolts being less than the cross-sectional area of said holes whereby free lateral of said tie rod is permitted.

No references cited. 

